Cellulosic biomass, which is available at low cost and in large abundance, is one of the only foreseeable sustainable sources for organic fuels, chemicals and materials (Lynd et al., 2005; Lynd et al., 2002, Lynd et al., 1999). In particular, ethanol production from cellulosic biomass has near-zero greenhouse emissions and offers many other environmental benefits (Lynd et al., 2005; Lynd et al., 1999; Lynd et al., 1991). The primary obstacle impeding production of ethanol and other chemicals from cellulosic biomass is the lack of technology for low-cost production (Lynd et al., 1999).
Traditional biochemical platforms or methods for fuel- and chemical-production generate sugars from cellulosic feedstock as reactive intermediates. These sugars can then be fermented to produce fuels and chemicals. There are five key steps involved in the current biochemical platform: (1) pre-treatment, (2) cellulase production, (3) enzymatic hydrolysis, (4) fermentation, and (5) product recovery. The first three steps: pre-treatment, cellulase production, and enzymatic hydrolysis are the three most costly steps in the production process, constituting approximately 65% of the overall processing cost.
The first step, pre-treatment, is a process to remove hemicellulose and lignin to increase the susceptibility of cellulose to subsequent enzymatic hydrolysis, thus allowing the exposed cellulose to be hydrolyzed into sugars by cellulases. The pre-treatment process tends to be thermo-chemical. Techniques used in the process include treatment with acid or base, or through steam or ammonia explosions. Most of the techniques are energy-intensive, expensive, and often polluting. In addition, capital cost for pre-treatment reactors are extremely high due to specific material requirements for acid or alkali resistance at elevated temperatures.
After the pre-treatment step, cellulases are added in a second step to hydrolyze cellulose, resulting in the production of sugars. While cellulase production costs have dropped significantly due to industrial production of enzymes, costs of this step still remain high. Lowering the processing costs of the two aforementioned steps is crucial for the realization of cost-effective production of ethanol and chemicals from biomass. Thus, there exists a need for improved compositions and methods for conversion of cellulosic biomass into commodity chemicals.